Design and Analysis of a Variable Buoyancy System for Efficient Hovering Control of Underwater Vehicles with State Feedback Controller

Abstract

The design process for Variable Buoyancy System (VBS) is not known in full, and existing approaches are not scalable. Furthermore, almost all the small size Autonomous Underwater Vehicles/Gliders (AUVs/G's) use very low capacity of buoyancy change (in the range of few milliliters) and the large size AUVs require large buoyancy change. Especially for adverse weather conditions, emergency recovery or defense-related applications, higher rate of rising/sinking (heave velocity) is needed along with an ability to hover at certain depth of operation. Depth of UVs can be controlled either by changing the displaced volume or by changing the overall weight and, herein, our focus is on the later. This article presents the problem of design and analysis of VBS for efficient hovering control of underwater vehicles at desired depth using the state feedback controller. We formulate and analyze the design and analysis approach of VBS using the fundamental of mechanics, system dynamics integration and control theory. Buoyancy is controlled by changing the overall weight of the vehicle using the ballasting/de-ballasting of water in ballast tanks through the use of Positive Displacement Pump (PDP) for control in heave velocity and hovering depth. Furthermore, detailed mass metric analysis of scalable design of VBS for different buoyancy capacities is performed to analyze the overall performance of the VBS. Also, the performances of AUVs integrated with VBS of different buoyancy capacities are investigated in both the open loop and closed loop with the LQR state feedback controller. Hovering performance results are presented for three Design Examples (DEs) of AUVs with 2.8 m, 4.0 m and 5.0 m length and they are integrated with various buoyancy capacities at 9 kg/min rate of change of buoyancy. Results indicate that the AUVs achieve the desired depth with almost negligible steady state error and when they reach the desired hovering depth of 400 m the maximum pitch angle achieved of 16.5 degree for all the Des is observed. Maximum heave velocity achieved during sinking is 0.44 m/s and it reduces to zero when the vehicle reaches the desired depth of hovering. The presented computer simulation results indicate good performance and demonstrate that the designed VBS is effective and efficient in changing the buoyancy, controlling and maintaining the depth, controlling the heave velocity and can be used in rescue/attack operations of both the civil and defense UVs.Keywords: variable buoyancy system (VBS); autonomous underwater vehicle (AUV); positive displacement pump (PDP); brush-less direct current (BLDC) motor; linear quadratic controller (LQR)This scene demands vehicles that can be used for surveying the oceans for high endurance and operable at high depths. These requirements have motivated the researchers to design and develop new age Underwater Vehicles (UVs). UVs are designed to perform underwater survey missions such as detecting and mapping submerged wrecks, rocks and obstructions that can pose a hazard, primarily for efficient ...

Analysis of Novel Assistive Robotic Multi‐Stage Underwater Lift Design for Swimmer Safety

“…The swimming pool movable elevator floor is made up of a mix of iron frames and a sheet of Thermocol whose density is almost negligible. Based on Archimedes' principle and a reference [32,33], the elevator platform will experience enormous buoyancy force which is the motive force that will undoubtedly lift the victim automatically with greater speed due to buoyancy. The mathematics involved in the calculation of the resultant buoyancy is as follows considering the materials used in the construction of the proposed system.…”

Design and extensibility analysis of a variable buoyancy system for small autonomous underwater vehicles

“…In Liu et al (2015), a hydraulic buoyancy system based on a swash-plate type axial piston pump was developed. In Zhang et al (2022) and Tiwari and Sharma (2020), an oil bladder-style hydraulic VBS for deep-sea undersea vehicles was proposed, with a positive displacement pump controlling the lift rate and hover depth. Electro-hydraulic methods have significant advantages in environments with large amounts of buoyancy change or operating depth, but the complexity of the structure and the large space required for installation make them challenging to incorporate into compact small AUVs.…”

Design and Experimental Tests of a Buoyancy Change Module for Autonomous Underwater Vehicles

“…Some details on the electric motor of the piston pump and on the hydraulic valve used are provided; however, no design insights on the reasons driving those choices are presented. In summary, none of the above-presented studies provides specific details on the mechanical development of the hull or on an informative choice of the components of the actuation devices, so the design process for BCMs is not known in full [19].…”